A common cleaning system used in the chemical industries is a pig cleaning system, also called a pigging system. “Pigging” involves pushing a solid or liquid through a section of piping with a “pig,” or plug, which is typically made of some sort of rubber, plastic, or foam, and that fits snugly inside the piping. The pushing of the pig inside of the piping is provided by a pressurized fluid, which may be a gas or liquid. The pig has a cylindrical shape, at least at a front portion and a rear portion thereof, in order to pass through similarly-shaped piping with the outer walls of the pig in close proximity or in contact with the inside surface of the walls of the piping.
Pigs are used in lube oil or paint blending to clean the pipes to avoid cross-contamination, and to empty the pipes into the product tanks (or sometimes to send a component back to its tank). Usually pigging is done at the beginning and at the end of each batch, but sometimes it is done in the midst of a batch, such as when producing a premix that will be used as an intermediate component.
The pigging system is frequently used for cleaning out the chemical product or contaminant in a manufacturing supply or product piping.